The E3 transcription unit of human adenoviruses (Ad) is a cassette of genes that counteracts host defenses. We propose to continue our studies on a subset of the E3 proteins. We will examine the properties and functions of these proteins using antisera, Ad E3 mutants, and Ad vectors and cell lines that express the E3 proteins individually. In collaborative animal model studies, we will ask how the E3 proteins affect inflammation induced by Ad-beta-galactosidase vectors, Ad pathogenesis in the mouse lung and liver, mouse poxvirus pathogenesis, and lung biology and virus pathogenesis in transgenic mice expressing the E3 proteins. Major effort will be placed on identifying cellular proteins that bind to the E3 proteins. E3-11.6K is a novel protein that promotes cell death. We will mutagenize the "death domain" of 11.6K, and ask whether 11.6K (i) acts alone to promote death, (ii) interacts with Ad E1B-19K and other proteins, and (iii) localizes to the inner or outer nuclear membrane. E3-gp19K binds to MHC class l antigens and blocks their transport from the endoplasmic reticulum (ER). We will ask whether (i) gp19K from different Ad subgroups binds with different affinities to different class l antigens, (ii) the "conserved face" of the alpha-helical transmembrane domain mediates protein-protein interactions, and (iii) why gp19K mutants have large plaques. We will ask whether the E3-6.7K ER membrane glycoprotein blocks TAP1/TAP2-mediated peptide transport into the ER. We will attempt to identify cellular proteins that bind to the E3-12.5K cytosolic protein. We have identified unique 20.5K, 20.1 K, and 16K E3 membrane proteins from Ad subgroup B Ad7. We propose to identify unique 29.8K, 27.2K, and l9K E3 membrane proteins from subgroup E Ad4, and a unique 61 K membrane protein from subgroup D Ad9. The properties and functions of these unique proteins will be analyzed. These studies will help us understand the molecular basis of Ad pathogenesis, they are important to the design of Ad vectors, and the E3 proteins themselves may by exploited as therapeutics to prevent inflammation or, in the case of 11.6K, to destroy breast, prostate, or other cancer cells.